Significance of repeatability

• Significant repeatability facilitates the study of selection acting on natural populations and the concept has several practical implications for identifying traits.
• Repeatability can set the upper limit to heritability. This is potentially a very useful interpretation of the repeatability of traits measured on natural populations because often, estimates of heritability cannot be obtained.
• Repeatability estimates may not set an upper limit to heritability if: (a) measured traits are not genetically identical, (b) common environmental effects work in opposition to direct genetic effects, (c) the temporary environments for each trait are negatively correlated, (d) significant genotype–environment interaction is present, or (e) the traits are influenced by maternal effects.

Ways to Improve Heritability and Repeatability

• Predict BV as accurately as possible to minimize mistakes in replacement selection.
• Predict PA as accurately as possible to minimize mistakes in culling.
• Emphasize environmental uniformity through good management (i.e., manage all animals as consistently as possible to minimize environmental variation or bias). Provide “codes” on data recording sheets for different “contemporary” management groups (e.g., creep feed and pastures) to avoid bias.
• Use mathematical adjustments for known environmental effects (e.g., WWADJ), which reduces total phenotypic variance and also avoids bias.